Re: printing gum on glass (for Marek)
Hmm, interesting question. I actually used doubled my usual
dichromate "load" for this experiment yesterday; instead of 1 unit
saturated ammonium dichromate: 1 unit gum/pigment, I used 2 units
saturated ammonium dichromate: 1 unit gum/pigment. I had gotten
intrigued lately, as a result of a discussion on another forum, with
Demachy's suggestion to use more dichromate solution when working
with a heavily-pigmented mix, so I've been trying that lately with
PBk11 (magnetic or iron oxide black) which is a fairly weak pigment
that takes a lot of pigment to make a solid black. Since that's the
pigment I picked to use for the glass experiment, and since my stock
mix of that pigment is very heavily pigmented and stiff, I went
ahead and tried it that way again.
If you go the other way, to less dichromate, it will be interesting
to compare results.
Katharine
On Jul 27, 2007, at 10:49 AM, Marek Matusz wrote:
Katharine,
It has been raining here no-stop and I have not done any printing
yet. I am wondering about the dichromate concentration. Typical gum
practice for paper printing uses fairly high dichromate
concentrations. I was wondering if much lower concentrations would
work beeter for the back exposure. Something more in line with
carbon printing. I have to look up the data for back exposure on
transparency that I have done last year.
Marek
From: Katharine Thayer <kthayer@pacifier.com>
Reply-To: alt-photo-process-l@usask.ca
To: alt-photo-process-l@usask.ca
Subject: Re: printing gum on glass (for Marek)
Date: Fri, 27 Jul 2007 10:14:25 -0700
>Hi marek,
>Yesterday I printed gum on glass with sun exposure from the back.
> I used plain glass that wasn't treated with any sub, or even
>cleaned particular scrupulously for that matter, exposed for one
>minute, and the gum adhered to the glass quite well; there was no
>flaking or frilling of the hardened gum layer. But the layer was
>so well exposed that there was no image even beginning to appear
>after two hours soaking, and I needed the sink for something else,
>so I started brushing away at the gum to see if I could get the
>image to come out. The initial gentle brushing seemed to be
>revealing a continuous tone image that wasn't noticeably softer
>than the same image printed on paper, but then I brushed too hard
>and brushed the image right off the glass. I'll have to try this
>again if the sun comes out again this afternoon.
>Katharine
>
>
>
>On Jul 19, 2007, at 7:34 AM, Katharine Thayer wrote:
>
>>Hi Marek,
>>Hope it stops raining soon.
>>
>>I was pretty sure I had reported that experiment to the list at the
>> time, so I went to the archives and searched for the post to
>>refresh my memory about the particulars. but couldn't find it.
>>
>>Anyway, I don't remember the details exactly, and I must not have
>>kept that experiment since it wasn't among the gum prints on glass
>>that I unpacked the other day; I must have scraped the gum off the
>>glass and re-used it. It may be that I did that print inside
>>under the photoflood bulb rather than outside under the sun; I just
>> don't remember. I think there's nothing for it but I'll have to
>>do it again to be sure. It's been raining here this week too,
>>although we had a couple of 100-degree days last week (that would
>>have been the time to do this experiment).
>>
>>Katharine
>>
>>
>>
>>
>>On Jul 19, 2007, at 6:50 AM, Marek Matusz wrote:
>>
>>
>>>Katharine,
>>>
>>>My typical dichromate concentrations are usuallu lower, for 1
>>>volume of 14 baume gum/pigment I use 1/2 to 1/3 volume of
>>>saturated ammonium dichromate solution. The dichromate
>>>concentration definitely changes exposure, but I would say you
>>>ball park estimate of yours and mine of about 1 minute sun
>>>exposure would be a good starting point. It has been raining in
>>>Houston forever and I am keeping my fingers crossed for this
>>>weekend to get some sun.
>>>
>>>I was surprized by your comment that you lost sharpness with back
>>>exposure through the glass. DIrect sun creates such a sharp shadow
>>> edge that I thought there should be no sharpness loss over a
>>>thin piece of glass. I guess the experimentation will show.
>>>Thanks for your comments.
>>>
>>>Marek
>>>
>>>From: Katharine Thayer <kthayer@pacifier.com>
>>>Reply-To: alt-photo-process-l@usask.ca
>>>To: alt-photo-process-l@usask.ca
>>>Subject: Re: printing gum on glass
>>>Date: Wed, 18 Jul 2007 00:17:59 -0700
>>> >Marek, what dichromate concentration are you using? that would
>>>make
>>> > a difference, of course, to the exposure . Also, the
>>>variation in
>>> > intensity from place to place. If I remember right; you're in
>>> >Houston? Your sun is probably more intense than mine in the
>>>Pacific
>>> > Northwest. I lived on the coast when I last did exposures in
>>>the
>>> >sun for gum on glass; as I recall they were a minute or less
>>>with a
>>> > fairly heavily pigmented mix of lamp black; that's with
>>>saturated
>>> >ammonium dichromate.
>>> >
>>> >I tried exposing from the back on regular picture glass, after
>>>our
>>> >thread about back-exposing on plastic a year ago or more, and
>>>found
>>> >that while the exposure worked well (the gum adhered well to the
>>> >glass with back-exposure) the thickness of the glass between
>>>the
>>> >negative and the gum resulted in a loss of sharpness and detail,
>>> >which didn't work very well with the image I chose. I still
>>>think
>>> >that's the best way to go for printing on glass, as you say, but
>>>it
>>> >needs to be the right kind of image that won't suffer too much
>>>from
>>> >not having direct contact between the negative and the emulsion;
>>> >perhaps a composition depending on abstract shapes rather than
>>>fine
>>> >detail.
>>> >Katharine
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >
>>> >On Jul 17, 2007, at 11:59 AM, Marek Matusz wrote:
>>> >
>>> >>Chris
>>> >>
>>> >>Good to hear the list is alive. I will miss the APIS activities
>>> >>this year. I really wanted to go this year, but something came
>>>up
>>> >>last moment. As far as the gum on glass I have tried it last
>>> >>summer. I made a couple of very thin blue layers for the
>>> >>preparation for tricolour gums. With very thin layers my
>>>exposures
>>> >>were short, and I remember long development times as well. I do
>>>not
>>> >> think I optimised it. The project was never finished as one
>>>day
>>> >>my stack of plates crashed and I never started again. I was
>>>very
>>> >>tempted to do some gum on glass with the back exposure. This
>>>should
>>> >> give a nice continuous gum layer sticking to the glass. If
>>>you
>>> >>have a colimated UV light source that would be the ideal way
>>>to
>>> >>make gum on glass. Direct sun exposure is another possibility,
>>> >>which I might try this weekend. What is the typical direct sun
>>> >>exposure (not in the shadow) if anybody is using this method.
>>>A
>>> >>good guess would save some calibration tests.
>>> >>
>>> >>Marek Matusz
>>> >>
>>> >>
>>> >>
>>>
>>>More photos, more messages, more storage—get 2GB with Windows Live
>>> Hotmail.
>>>
>>
>>
>
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